The condensation of a hydroxy-containing compound with an amine to liberate water is well known. In many instances, the condensation has been effected by using an acid catalyst, such as a phosphorus-containing compound. The ability to effect intermolecular condensation of a hydroxy-containing compound with an amine has been of substantial interest in the preparation of polyalkylene polyamines, particularly polyethylene polyamines.
A variety of polyalkylene polyamines can be formed by the basic reaction of the hydroxy compound and amine compound. However, one of the objectives in the preparation of polyalkylene polyamines has been to maximize the intermolecular condensation to form the linear or noncyclic polyalkylene polyamine as opposed to effecting an intramolecular condensation of such compounds which convert to the cyclic amine. The former amines are utilized in preparing lubricant formulations, acid gas scrubbing compositions, and the like. Numerous patents have issued since the 1960's which illustrate various embodiments for preparing linear polyalkylene polyamines in high selectivity by reacting an alkylene amine and an alkanolamine in the presence of an acidic catalyst. Representative patents include:
Meuly, U.S. Pat. No. 3,121,115, discloses the reaction of an amine with an alkanolamine in the presence of a phosphorus-containing compound to produce alkylated amines. Reaction conditions used were 200.degree.-350.degree. C. and pressures ranged from atmospheric to super atmospheric.
U.S. Pat. No. 4,036,881 discloses the preparation of polyalkylene polyamines, particularly polyethylene polyamines, by the reaction of monoethanolamine and ethylenediamine under liquid phase conditions. An acidic phosphorus-containing compound was utilized to effect catalysis of the reaction. Representative catalyst systems included alkyl and aryl phosphinic acids, phosphoric and phosphorous acid compounds and their anhydrides, and metal phosphates such as iron, aluminum and boron phosphate and so forth. The patentees pointed out that it was important to maintain liquid phase conditions in the reaction zone for achieving high selectivity to linear polyethylene polyamines. If vapor phase conditions were encountered, as shown in Example 12, then selectivity to linear polyethylene polyamines was sacrificed.
Other patents which show the preparation of polyethylene polyamines or broadly, polyalkylene polyamines under liquid phase conditions include U.S. Pat. No. 4,394,524; 4,399,308; 4,362,886; 4,314,083; and European patent application Nos. 0,093,434 and 0,093,983.
The above patents describe various processes for producing polyalkylene polyamines using a variety of acidic catalytic systems such as, for example, Lewis acids, arsenic, antimony or bismuth salts; a variety of phosphorus containing catalyst systems including phosphoric acid, boron phosphate as noted in the Brennan, et al., U.S. Pat. No. 4,036,881, and phosphoramides. Each of the processes involves the reaction of an alkanolamine with an alkylene amine compound at temperatures from about 175.degree.-300.degree. C., and preferably temperatures in excess of 225.degree. C. to produce linear polyalkylene polyamines. Each of the processes employs conditions which maintain the reactants in liquid phase, and thus the reaction pressure is controlled to the extent necessary to maintain such liquid phase conditions at reaction temperature.
U.S. Pat. No. 4,394,524 differs slightly from the processes described above in that ammonia is included as an additional reactant to convert alkanolamine to an alkylene amine in situ. With the utilization of ammonia, higher selectivities to polyethylene polyamines were reported. However, pressures were maintained such that the reaction was carried out in essentially liquid phase.
Although the above liquid phase processes result in producing linear polyalkylene polyamines in relatively high selectivity, the processes suffer from a series of processing disadvantages. The processing disadvantages arise because of the solubility of the catalyst systems in the reactants or reaction byproducts. This is particularly true in the case of phosphorous-containing catalytic compounds in that high proportions of phosphorous are recovered in the reaction product and must be removed. This is typically done by distillation. An additional problem associated with these processes is that the catalyst must be continually replaced or replenished.